# Patent

## Title
Methods and apparatus for three-dimensional nonvolatile memory

## Abstract

A method is provided that includes forming a dielectric material above a substrate, forming a hole in the dielectric material, the hole disposed in a first direction, forming a word line layer above the substrate via the hole, the word line layer disposed in a second direction perpendicular to the first direction, the word line layer including a first conductive material having a first work function, forming a nonvolatile memory material on a sidewall of the hole, the nonvolatile memory material including a semiconductor material layer and a conductive oxide material layer, forming a local bit line in the hole, the local bit line including a second conductive material having a second work function, wherein the first work function is greater than the second work function, and forming a memory cell comprising the nonvolatile memory material at an intersection of the local bit line and the word line layer.

## Background
BACKGROUND
Semiconductor memory is widely used in various electronic devices such as mobile computing devices, mobile phones, solid-state drives, digital cameras, personal digital assistants, medical electronics, servers, and non-mobile computing devices. Semiconductor memory may include non-volatile memory or volatile memory. A non-volatile memory device allows information to be stored or retained even when the non-volatile memory device is not connected to a power source.
One example of non-volatile memory uses memory cells that include reversible resistance-switching memory elements that may be set to either a low resistance state or a high resistance state. The memory cells may be individually connected between first and second conductors (e.g., a bit line electrode and a word line electrode). The state of such a memory cell is typically changed by proper voltages being placed on the first and second conductors.
In recent years, non-volatile memory devices have been scaled to reduce the cost per bit. However, as process geometries shrink, many design and process challenges are presented



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A depicts an embodiment of a memory system and a host.
FIG. 1B depicts an embodiment of memory core control circuits.
FIG. 1C depicts an embodiment of a memory core.
FIG. 1D depicts an embodiment of a memory bay.
FIG. 1E depicts an embodiment of a memory block.
FIG. 1F depicts another embodiment of a memory bay.
FIG. 2A depicts an embodiment of a portion of a monolithic three-dimensional memory array.
FIG. 2B depicts an embodiment of a portion of a monolithic three-dimensional memory array that includes vertical strips of a non-volatile memory material.
FIGS. 3A-3E depict various views of an embodiment monolithic three-dimensional memory array.
FIGS. 4A1-4J2 are cross-sectional views of a portion of a substrate during an example fabrication of the monolithic three-dimensional memory array of FIGS. 3A-3E.



DETAILED DESCRIPTION
Technology is described for forming monolithic three-dimensional nonvolatile memory arrays. In particular, technology is described for forming monolithic three-dimensional nonvolatile memory arrays that include reversible resistance-switching memory cells that include resistance-switching elements that include a semiconductor material layer and a conductive oxide material layer. Each reversible resistance-switching element is disposed between a word line and a bit line. The word line includes a first conductive material having a first work function, the bit line includes a second conductive material having a second work function, and the first work function is greater than the second work function.
An example method includes forming a dielectric material above a substrate, forming a hole in the dielectric material, the hole disposed in a first direction, forming a word line layer above the substrate via the hole, the word line layer disposed in a second direction perpendicular to the first direction, forming a nonvolatile memory material on a sidewall of the hole, forming a local bit line in the hole, and forming a memory cell including the nonvolatile memory material at an intersection of the local bit line and the word line layer. In an embodiment, the word line layer includes a first conductive material having a first work function, and the local bit line includes a second conductive material having a second work function, wherein the first work function is greater than the second work function.
In some embodiments, a memory array may include a cross-point memory array. A cross-point memory array may refer to a memory array in which two-terminal memory cells are placed at the intersections of a first set of control lines (e.g., word lines) arranged in a first direction and a second set of control lines (e.g., bit lines) arranged in a second direction perpendicular to the first direction. The two-terminal memory cells may include a reversible resistance-switching memory element disposed between first and second conductors. Example reversible resistance-switching memory elements include a phase change material, a ferroelectric material, a metal oxide (e.g., hafnium oxide), a barrier modulated switching structure, or other similar reversible resistance-switching memory elements.
Example barrier modulated switching structures include a semiconductor material layer adjacent a conductive oxide material layer (e.g., an amorphous silicon layer adjacent a crystalline titanium oxide layer). Other example barrier modulated switching structures include a thin (e.g., less than about 2 nm) barrier oxide material disposed between the semiconductor material layer and the conductive oxide material layer (e.g., an aluminum oxide layer disposed between an amorphous silicon layer and a crystalline titanium oxide layer). As used herein, a memory cell that includes a barrier modulated switching structure is referred to herein as a “barrier modulated cell” (BMC).
In some cases, each memory cell in a cross-point memory array includes a reversible resistance-switching memory element in series with a steering element or an isolation element, such as a diode, to reduce leakage currents. In other cross-point memory arrays, the memory cells do not include an isolation element.
In an embodiment, a non-volatile storage system may include one or more two-dimensional arrays of non-volatile memory cells. The memory cells within a two-dimensional memory array may form a single layer of memory cells and may be selected via control lines (e.g., word lines and bit lines) in the X and Y directions. In another embodiment, a non-volatile storage system may include one or more monolithic three-dimensional memory arrays in which two or more layers of memory cells may be formed above a single substrate without any intervening substrates.
In some cases, a three-dimensional memory array may include one or more vertical columns of memory cells located above and orthogonal to a substrate. In an example, a non-volatile storage system may include a memory array with vertical bit lines or bit lines that are arranged orthogonal to a semiconductor substrate. The substrate may include a silicon substrate. The memory array may include rewriteable non-volatile memory cells, wherein each memory cell includes a reversible resistance-switching memory element without an isolation element in series with the reversible resistance-switching memory element (e.g., no diode in series with the reversible resistance-switching memory element).
In some embodiments, a non-volatile storage system may include a non-volatile memory that is monolithically formed in one or more physical levels of arrays of memory cells having an active area disposed above a silicon substrate. The non-volatile storage system may also include circuitry associated with the operation of the memory cells (e.g., decoders, state machines, page registers, and/or control circuitry for controlling reading, programming and erasing of the memory cells). The circuitry associated with the operation of the memory cells may be located above the substrate or within the substrate.
In some embodiments, a non-volatile storage system may include a monolithic three-dimensional memory array. The monolithic three-dimensional memory array may include one or more levels of memory cells. Each memory cell within a first level of the one or more levels of memory cells may include an active area that is located above a substrate (e.g., above a single-crystal substrate or a crystalline silicon substrate). In one example, the active area may include a semiconductor junction (e.g., a P-N junction). The active area may include a portion of a source or drain region of a transistor. In another example, the active area may include a channel region of a transistor.
FIG. 1A depicts one embodiment of a memory system 100 and a host 102. Memory system 100 may include a non-volatile storage system interfacing with host 102 (e.g., a mobile computing device). In some cases, memory system 100 may be embedded within host 102. In other cases, memory system 100 may include a memory card. As depicted, memory system 100 includes a memory chip controller 104 and a memory chip 106. Although a single memory chip 106 is depicted, memory system 100 may include more than one memory chip (e.g., four, eight or some other number of memory chips). Memory chip controller 104 may receive data and commands from host 102 and provide memory chip data to host 102.
Memory chip controller 104 may include one or more state machines, page registers, SRAM, and control circuitry for controlling the operation of memory chip 106. The one or more state machines, page registers, SRAM, and control circuitry for controlling the operation of memory chip 106 may be referred to as managing or control circuits. The managing or control circuits may facilitate one or more memory array operations, such as forming, erasing, programming, and reading operations.
In some embodiments, the managing or control circuits (or a portion of the managing or control circuits) for facilitating one or more memory array operations may be integrated within memory chip 106. Memory chip controller 104 and memory chip 106 may be arranged on a single integrated circuit. In other embodiments, memory chip controller 104 and memory chip 106 may be arranged on different integrated circuits. In some cases, memory chip controller 104 and memory chip 106 may be integrated on a system board, logic board, or a PCB.
Memory chip 106 includes memory core control circuits 108 and a memory core 110. Memory core control circuits 108 may include logic for controlling the selection of memory blocks (or arrays) within memory core 110, controlling the generation of voltage references for biasing a particular memory array into a read or write state, and generating row and column addresses.
Memory core 110 may include one or more two-dimensional arrays of memory cells or one or more three-dimensional arrays of memory cells. In an embodiment, memory core control circuits 108 and memory core 110 are arranged on a single integrated circuit. In other embodiments, memory core control circuits 108 (or a portion of memory core control circuits 108) and memory core 110 may be arranged on different integrated circuits.
A memory operation may be initiated when host 102 sends instructions to memory chip controller 104 indicating that host 102 would like to read data from memory system 100 or write data to memory system 100. In the event of a write (or programming) operation, host 102 will send to memory chip controller 104 both a write command and the data to be written. The data to be written may be buffered by memory chip controller 104 and error correcting code (ECC) data may be generated corresponding with the data to be written. The ECC data, which allows data errors that occur during transmission or storage to be detected and/or corrected, may be written to memory core 110 or stored in non-volatile memory within memory chip controller 104. In an embodiment, the ECC data are generated and data errors are corrected by circuitry within memory chip controller 104.
Memory chip controller 104 controls operation of memory chip 106. In one example, before issuing a write operation to memory chip 106, memory chip controller 104 may check a status register to make sure that memory chip 106 is able to accept the data to be written. In another example, before issuing a read operation to memory chip 106, memory chip controller 104 may pre-read overhead information associated with the data to be read. The overhead information may include ECC data associated with the data to be read or a redirection pointer to a new memory location within memory chip 106 in which to read the data requested. Once a read or write operation is initiated by memory chip controller 104, memory core control circuits 108 may generate the appropriate bias voltages for word lines and bit lines within memory core 110, and generate the appropriate memory block, row, and column addresses.
In some embodiments, one or more managing or control circuits may be used for controlling the operation of a memory array. The one or more managing or control circuits may provide control signals to a memory array to perform an erase operation, a read operation, and/or a write operation on the memory array. In one example, the one or more managing or control circuits may include any one of or a combination of control circuitry, state machine, decoders, sense amplifiers, read/write circuits, and/or controllers. The one or more managing circuits may perform or facilitate one or more memory array operations including erasing, programming, or reading operations. In one example, one or more managing circuits may include an on-chip memory controller for determining row and column address, word line and bit line addresses, memory array enable signals, and data latching signals.
FIG. 1B depicts one embodiment of memory core control circuits 108. As depicted, memory core control circuits 108 include address decoders 120, voltage generators for first control lines 122, voltage generators for second control lines 124 and signal generators for reference signals 126 (described in more detail below). Control lines may include word lines, bit lines, or a combination of word lines and bit lines. First control lines may include first (e.g., selected) word lines and/or first (e.g., selected) bit lines that are used to place memory cells into a first (e.g., selected) state. Second control lines may include second (e.g., unselected) word lines and/or second (e.g., unselected) bit lines that are used to place memory cells into a second (e.g., unselected) state.
Address decoders 120 may generate memory block addresses, as well as row addresses and column addresses for a particular memory block. Voltage generators (or voltage regulators) for first control lines 122 may include one or more voltage generators for generating first (e.g., selected) control line voltages. Voltage generators for second control lines 124 may include one or more voltage generators for generating second (e.g., unselected) control line voltages. Signal generators for reference signals 126 may include one or more voltage and/or current generators for generating reference voltage and/or current signals.
FIGS. 1C-1F depict one embodiment of a memory core organization that includes a memory core having multiple memory bays, and each memory bay having multiple memory blocks. Although a memory core organization is disclosed where memory bays include memory blocks, and memory blocks include a group of memory cells, other organizations or groupings also can be used with the technology described herein.
FIG. 1C depicts an embodiment of memory core 110 of FIG. 1A. As depicted, memory core 110 includes memory bay 130 and memory bay 132. In some embodiments, the number of memory bays per memory core can differ for different implementations. For example, a memory core may include only a single memory bay or multiple memory bays (e.g., 16 or other number of memory bays).
FIG. 1D depicts an embodiment of memory bay 130 in FIG. 1C. As depicted, memory bay 130 includes memory blocks 140-144 and read/write circuits 146. In some embodiments, the number of memory blocks per memory bay may differ for different implementations. For example, a memory bay may include one or more memory blocks (e.g., 32 or other number of memory blocks per memory bay). Read/write circuits 146 include circuitry for reading and writing memory cells within memory blocks 140-144.
As depicted, read/write circuits 146 may be shared across multiple memory blocks within a memory bay. This allows chip area to be reduced because a single group of read/write circuits 146 may be used to support multiple memory blocks. However, in some embodiments, only a single memory block may be electrically coupled to read/write circuits 146 at a particular time to avoid signal conflicts.
In some embodiments, read/write circuits 146 may be used to write one or more pages of data into memory blocks 140-144 (or into a subset of the memory blocks). The memory cells within memory blocks 140-144 may permit direct over-writing of pages (i.e., data representing a page or a portion of a page may be written into memory blocks 140-144 without requiring an erase or reset operation to be performed on the memory cells prior to writing the data).
In one example, memory system 100 of FIG. 1A may receive a write command including a target address and a set of data to be written to the target address. Memory system 100 may perform a read-before-write (RBW) operation to read the data currently stored at the target address and/or to acquire overhead information (e.g., ECC information) before performing a write operation to write the set of data to the target address.
In some cases, read/write circuits 146 may be used to program a particular memory cell to be in one of three or more data/resistance states (i.e., the particular memory cell may include a multi-level memory cell). In one example, read/write circuits 146 may apply a first voltage difference (e.g., 2V) across the particular memory cell to program the particular memory cell into a first state of the three or more data/resistance states or a second voltage difference (e.g., 1V) across the particular memory cell that is less than the first voltage difference to program the particular memory cell into a second state of the three or more data/resistance states.
Applying a smaller voltage difference across the particular memory cell may cause the particular memory cell to be partially programmed or programmed at a slower rate than when applying a larger voltage difference. In another example, read/write circuits 146 may apply a first voltage difference across the particular memory cell for a first time period to program the particular memory cell into a first state of the three or more data/resistance states, and apply the first voltage difference across the particular memory cell for a second time period less than the first time period. One or more programming pulses followed by a memory cell verification phase may be used to program the particular memory cell to be in the correct state.
FIG. 1E depicts an embodiment of memory block 140 in FIG. 1D. As depicted, memory block 140 includes a memory array 150, row decoder 152, and column decoder 154. Memory array 150 may include a contiguous group of memory cells having contiguous word lines and bit lines. Memory array 150 may include one or more layers of memory cells. Memory array 150 may include a two-dimensional memory array or a three-dimensional memory array.
Row decoder 152 decodes a row address and selects a particular word line in memory array 150 when appropriate (e.g., when reading or writing memory cells in memory array 150). Column decoder 154 decodes a column address and selects one or more bit lines in memory array 150 to be electrically coupled to read/write circuits, such as read/write circuits 146 in FIG. 1D. In one embodiment, the number of word lines is 4K per memory layer, the number of bit lines is 1K per memory layer, and the number of memory layers is 4, providing a memory array 150 containing 16M memory cells.
FIG. 1F depicts an embodiment of a memory bay 134. Memory bay 134 is an alternative example implementation for memory bay 130 of FIG. 1D. In some embodiments, row decoders, column decoders, and read/write circuits may be split or shared between memory arrays. As depicted, row decoder 152b is shared between memory arrays 150a and 150b because row decoder 152b controls word lines in both memory arrays 150a and 150b (i.e., the word lines driven by row decoder 152b are shared).
Row decoders 152a and 152b may be split such that even word lines in memory array 150a are driven by row decoder 152a and odd word lines in memory array 150a are driven by row decoder 152b. Row decoders 152c and 152b may be split such that even word lines in memory array 150b are driven by row decoder 152c and odd word lines in memory array 150b are driven by row decoder 152b. 
Column decoders 154a and 154b may be split such that even bit lines in memory array 150a are controlled by column decoder 154b and odd bit lines in memory array 150a are driven by column decoder 154a. Column decoders 154c and 154d may be split such that even bit lines in memory array 150b are controlled by column decoder 154d and odd bit lines in memory array 150b are driven by column decoder 154c. 
The selected bit lines controlled by column decoder 154a and column decoder 154c may be electrically coupled to read/write circuits 146a. The selected bit lines controlled by column decoder 154b and column decoder 154d may be electrically coupled to read/write circuits 146b. Splitting the read/write circuits into read/write circuits 146a and 146b when the column decoders are split may allow for a more efficient layout of the memory bay.
FIG. 2A depicts one embodiment of a portion of a monolithic three-dimensional memory array 200 that includes a first memory level 210, and a second memory level 212 positioned above first memory level 210. Memory array 200 is one example of an implementation for memory array 150 of FIG. 1E. Local bit lines LBL11-LBL33 are arranged in a first direction (e.g., a vertical or z-direction) and word lines WL10-WL23 are arranged in a second direction (e.g., an x-direction) perpendicular to the first direction. This arrangement of vertical bit lines in a monolithic three-dimensional memory array is one embodiment of a vertical bit line memory array.
As depicted, disposed between the intersection of each local bit line and each word line is a particular memory cell (e.g., memory cell M111 is disposed between local bit line LBL11 and word line WL10). The particular memory cell may include a floating gate memory element, a charge trap memory element (e.g., using a silicon nitride material), a reversible resistance-switching memory element, or other similar device. The global bit lines GBL1-GBL3 are arranged in a third direction (e.g., a y-direction) that is perpendicular to both the first direction and the second direction.
Each local bit line LBL11-LBL33 has an associated bit line select transistor Q11-Q33, respectively. Bit line select transistors Q11-Q33 may be field effect transistors, such as shown, or may be any other transistors. As depicted, bit line select transistors Q11-Q31 are associated with local bit lines LBL11-LBL31, respectively, and may be used to connect local bit lines LBL11-LBL31 to global bit lines GBL1-GBL3, respectively, using row select line SG1. In particular, each of bit line select transistors Q11-Q31 has a first terminal (e.g., a drain/source terminal) coupled to a corresponding one of local bit lines LBL11-LBL31, respectively, a second terminal (e.g., a source/drain terminal) coupled to a corresponding one of global bit lines GBL1-GBL3, respectively, and a third terminal (e.g., a gate terminal) coupled to row select line SG1.
Similarly, bit line select transistors Q12-Q32 are associated with local bit lines LBL12-LBL32, respectively, and may be used to connect local bit lines LBL12-LBL32 to global bit lines GBL1-GBL3, respectively, using row select line SG2. In particular, each of bit line select transistors Q12-Q32 has a first terminal (e.g., a drain/source terminal) coupled to a corresponding one of local bit lines LBL12-LBL32, respectively, a second terminal (e.g., a source/drain terminal) coupled to a corresponding one of global bit lines GBL1-GBL3, respectively, and a third terminal (e.g., a gate terminal) coupled to row select line SG2.
Likewise, bit line select transistors Q13-Q33 are associated with local bit lines LBL13-LBL33, respectively, and may be used to connect local bit lines LBL13-LBL33 to global bit lines GBL1-GBL3, respectively, using row select line SG3. In particular, each of bit line select transistors Q13-Q33 has a first terminal (e.g., a drain/source terminal) coupled to a corresponding one of local bit lines LBL13-LBL33, respectively, a second terminal (e.g., a source/drain terminal) coupled to a corresponding one of global bit lines GBL1-GBL3, respectively, and a third terminal (e.g., a gate terminal) coupled to row select line SG3.
Because a single bit line select transistor is associated with a corresponding local bit line, the voltage of a particular global bit line may be selectively applied to a corresponding local bit line. Therefore, when a first set of local bit lines (e.g., LBL11-LBL31) is biased to global bit lines GBL1-GBL3, the other local bit lines (e.g., LBL12-LBL32 and LBL13-LBL33) must either also be driven to the same global bit lines GBL1-GBL3 or be floated.
In an embodiment, during a memory operation, all local bit lines within the memory array are first biased to an unselected bit line voltage by connecting each of the global bit lines to one or more local bit lines. After the local bit lines are biased to the unselected bit line voltage, then only a first set of local bit lines LBL11-LBL31 are biased to one or more selected bit line voltages via the global bit lines GBL1-GBL3, while the other local bit lines (e.g., LBL12-LBL32 and LBL13-LBL33) are floated. The one or more selected bit line voltages may correspond with, for example, one or more read voltages during a read operation or one or more programming voltages during a programming operation.
In an embodiment, a vertical bit line memory array, such as memory array 200, includes a greater number of memory cells along the word lines as compared with the number of memory cells along the vertical bit lines (e.g., the number of memory cells along a word line may be more than 10 times the number of memory cells along a bit line). In one example, the number of memory cells along each bit line may be 16 or 32, whereas the number of memory cells along each word line may be 2048 or more than 4096. Other numbers of memory cells along each bit line and along each word line may be used.
In an embodiment of a read operation, the data stored in a selected memory cell (e.g., memory cell M111) may be read by biasing the word line connected to the selected memory cell (e.g., selected word line WL10) to a selected word line voltage in read mode (e.g., 0V). The local bit line (e.g., LBL11) coupled to the selected memory cell (M111) is biased to a selected bit line voltage in read mode (e.g., 1 V) via the associated bit line select transistor (e.g., Q11) coupled to the selected local bit line (LBL11), and the global bit line (e.g., GBL1) coupled to the bit line select transistor (Q11). A sense amplifier may then be coupled to the selected local bit line (LBL11) to determine a read current IREAD of the selected memory cell (M111). The read current IREAD is conducted by the bit line select transistor Q11, and may be between about 100 nA and about 500 nA, although other read currents may be used.
In an embodiment of a write operation, data may be written to a selected memory cell (e.g., memory cell M221) by biasing the word line connected to the selected memory cell (e.g., WL20) to a selected word line voltage in write mode (e.g., 5V). The local bit line (e.g., LBL21) coupled to the selected memory cell (M221) is biased to a selected bit line voltage in write mode (e.g., 0 V) via the associated bit line select transistor (e.g., Q21) coupled to the selected local bit line (LBL21), and the global bit line (e.g., GBL2) coupled to the bit line select transistor (Q21). During a write operation, a programming current IPGRM is conducted by the associated bit line select transistor Q21, and may be between about 3 uA and about 6 uA, although other programming currents may be used.
During the write operation described above, the word line (e.g., WL20) connected to the selected memory cell (M221) may be referred to as a “selected word line,” and the local bit line (e.g., LBL21) coupled to the selected memory cell (M221) be referred to as the “selected local bit line.” All other word lines coupled to unselected memory cells may be referred to as “unselected word lines,” and all other local bit lines coupled to unselected memory cells may be referred to as “unselected local bit lines.” For example, if memory cell M221 is the only selected memory cell in memory array 200, word lines WL10-WL13 and WL21-WL23 are unselected word lines, and local bit lines LBL11, LBL31, LBL12-LBL32, and LBL13-LBL33 are unselected local bit lines.
FIG. 2B depicts an embodiment of a portion of a monolithic three-dimensional memory array 202 that includes vertical strips of a non-volatile memory material. The portion of monolithic three-dimensional memory array 202 depicted in FIG. 2B may include an implementation for a portion of the monolithic three-dimensional memory array 200 depicted in FIG. 2A.
Monolithic three-dimensional memory array 202 includes word lines WL10, WL11, WL12, . . . , WL42 that are formed in a first direction (e.g., an x-direction), vertical bit lines LBL11, LBL12, LBL13, . . . , LBL23 that are formed in a second direction perpendicular to the first direction (e.g., a z-direction), and vertical strips of non-volatile memory material 214 formed in the second direction (e.g., the z-direction). A spacer 216 made of a dielectric material (e.g., silicon dioxide, silicon nitride, or other dielectric material) is disposed between adjacent word lines WL10, WL11, WL42, . . . , WL42.
Each vertical strip of non-volatile memory material 214 may include, for example, a vertical oxide material, a vertical reversible resistance-switching memory material (e.g., one or more metal oxide layers such as nickel oxide, hafnium oxide, or other similar metal oxide materials, a phase change material, a barrier modulated switching structure or other similar reversible resistance-switching memory material), a ferroelectric material, or other non-volatile memory material.
Each vertical strip of non-volatile memory material 214 may include a single material layer or multiple material layers. In an embodiment, each vertical strip of non-volatile memory material 214 includes a vertical barrier modulated switching structure. Example barrier modulated switching structures include a semiconductor material layer adjacent a conductive oxide material layer (e.g., an amorphous silicon layer adjacent a crystalline titanium oxide layer). Other example barrier modulated switching structures include a thin (e.g., less than about 2 nm) barrier oxide material disposed between the semiconductor material layer and the conductive oxide material layer (e.g., an aluminum oxide layer disposed between an amorphous silicon layer and a crystalline titanium oxide layer). Such multi-layer embodiments may be used to form BMC memory elements.
In an embodiment, each vertical strip of non-volatile memory material 214 may include a single continuous layer of material that may be used by a plurality of memory cells or devices.
In an embodiment, portions of the vertical strip of the non-volatile memory material 214b may include a part of a first memory cell associated with the cross section between WL12 and LBL13 and a part of a second memory cell associated with the cross section between WL22 and LBL13. In some cases, a vertical bit line, such as LBL13, may include a vertical structure (e.g., a rectangular prism, a cylinder, or a pillar) and the non-volatile material may completely or partially surround the vertical structure (e.g., a conformal layer of phase change material surrounding the sides of the vertical structure).
As depicted, each of the vertical bit lines LBL11, LBL12, LBL13, . . . , LBL23 may be connected to one of a set of global bit lines via an associated vertically-oriented bit line select transistor (e.g., Q11, Q12, Q13, Q23). Each vertically-oriented bit line select transistor may include a MOS device (e.g., an NMOS device) or a vertical thin-film transistor (TFT).
In an embodiment, each vertically-oriented bit line select transistor is a vertically-oriented pillar-shaped TFT coupled between an associated local bit line pillar and a global bit line. In an embodiment, the vertically-oriented bit line select transistors are formed in a pillar select layer formed above a CMOS substrate, and a memory layer that includes multiple layers of word lines and memory elements is formed above the pillar select layer.
FIGS. 3A-3E depict various views of an embodiment of a portion of a monolithic three-dimensional memory array 300 that includes vertical strips of a non-volatile memory material. The physical structure depicted in FIGS. 3A-3E may include one implementation for a portion of the monolithic three-dimensional memory array depicted in FIG. 2B.
Monolithic three-dimensional memory array 300 includes vertical bit lines LBL11-LBL33 arranged in a first direction (e.g., a z-direction), word lines WL10, WL11, . . . , WL53 arranged in a second direction (e.g., an x-direction) perpendicular to the first direction, and row select lines SG1, SG2, SG3 arranged in the second direction, and global bit lines GBL1, GBL2, GBL3 arranged in a third direction (e.g., a y-direction) perpendicular to the first and second directions.
Vertical bit lines LBL11-LBL33 are disposed above global bit lines GBL1, GBL2, GBL3, which each have a long axis in the second (e.g., x-direction). Person of ordinary skill in the art will understand that monolithic three-dimensional memory arrays, such as monolithic three-dimensional memory array 300 may include more or fewer than twenty word lines, three row select lines, three global bit lines, and nine vertical bit lines.
In an embodiment, global bit lines GBL1, GBL2, GBL3 are disposed above a substrate 302, such as a silicon, germanium, silicon-germanium, undoped, doped, bulk, silicon-on-insulator (“SOI”) or other substrate with or without additional circuitry. In an embodiment, an isolation layer 304, such as a layer of silicon dioxide, silicon nitride, silicon oxynitride or any other suitable insulating layer, is formed above substrate 302.
In an embodiment, a first dielectric material layer 308 (e.g., silicon dioxide) and a second dielectric material layer 310 (e.g., silicon dioxide) are formed above isolation layer 304. Global bit lines GBL1, GBL2, GBL3 are disposed above isolation layer 304 and are separated from one another by first dielectric material layer 308.
Vertically-oriented bit line select transistors Q11-Q33 are disposed above global bit lines GBL1, GBL2, GBL3 and are separated from one another by second dielectric material layer 310. Vertically-oriented bit line select transistors Q11-Q13 are disposed above and electrically coupled to global bit line GBL1, vertically-oriented bit line select transistors Q21-Q23 are disposed above and electrically coupled to global bit line GBL2, and vertically-oriented bit line select transistors Q31-Q33 are disposed above and electrically coupled to global bit line GBL3.
Vertically-oriented bit line select transistors Q11-Q33 may be field effect transistors, although other transistors types may be used. In an embodiment, each of vertically-oriented bit line select transistors Q31-Q33 has a height between about 1500 angstroms and about 5000 angstroms. Other height values may be used.
Each of vertically-oriented bit line select transistors Q11-Q33 has a first terminal 312a (e.g., a drain/source terminal), a second terminal 312b (e.g., a source/drain terminal), a first control terminal 312c1 (e.g., a first gate terminal) and a second control terminal 312c2 (e.g., a second gate terminal). First gate terminal 312c1 and second gate terminal 312c2 may be disposed on opposite sides of the vertically-oriented bit line select transistor. A gate dielectric material 314 (e.g., SiO2) is disposed between first gate terminal 312c1 and first terminal 312a and second terminal 312b, and also is disposed between second gate terminal 312c2 and first terminal 312a and second terminal 312b. 
First gate terminal 312c1 may be used to selectively induce a first conductive channel between first terminal 312a and second terminal 312b of the transistor, and second gate terminal 312c2 may be used to selectively induce a second conductive channel between first terminal 312a and second terminal 312b of the transistor. In an embodiment, first gate terminal 312c1 and second gate terminal 312c2 are coupled together to form a single control terminal 312c that may be used to collectively turn ON and OFF the vertically-oriented bit line select transistor.
Row select lines SG1, SG2, SG3 are disposed above global bit lines GBL1, GBL2 and GBL3, and form gate terminals 312c of vertically-oriented bit line select transistors Q11-Q33. In particular, row select line SG1 forms the gate terminals of vertically-oriented bit line select transistors Q11, Q21 and Q31, row select line SG2 forms the gate terminals of vertically-oriented bit line select transistors Q12, Q22 and Q32, and row select line SG3 forms the gate terminals of vertically-oriented bit line select transistors Q13, Q23 and Q33.
A first etch stop layer 316 (e.g., aluminum oxide) is disposed above second dielectric material layer 310. A stack of word lines WL10, WL11, . . . , WL53 is disposed above first etch stop layer 316, with a third dielectric material layer 318 (e.g., silicon dioxide) separating adjacent word lines. A second etch stop layer 320 (e.g., polysilicon) may be formed above the stack of word lines WL10, WL11, . . . , WL53.
In an embodiment, vertical strips of a non-volatile memory material 214 are disposed adjacent word lines WL10, WL11, . . . , WL53. Vertical strips of non-volatile memory material 214 may be formed in the first direction (e.g., the z-direction). A vertical strip of non-volatile memory material 214 may include, for example, a vertical oxide layer, a vertical reversible resistance-switching material (e.g., one or more metal oxide layers such as nickel oxide, hafnium oxide, or other similar metal oxide materials, a phase change material, a barrier modulated switching structure or other similar reversible resistance-switching memory material), a ferroelectric material, or other non-volatile memory material.
A vertical strip of non-volatile memory material 214 may include a single continuous layer of material that may be used by a plurality of memory cells or devices. For simplicity, vertical strip of non-volatile memory material 214 will be referred to in the remaining discussion as reversible resistance-switching memory material 214.
Each vertical strip of non-volatile memory material 214 may include a single material layer or multiple material layers. In an embodiment, each vertical strip of non-volatile memory material 214 includes a vertical barrier modulated switching structure that includes a semiconductor material layer adjacent a conductive oxide material layer. In other embodiments, each vertical strip of non-volatile memory material 214 includes a vertical barrier modulated switching structure that includes a thin (e.g., less than about 2 nm) barrier oxide material disposed between a semiconductor material layer and a conductive oxide material layer.
In an embodiment, each vertical strip of non-volatile memory material 214 includes a barrier modulated switching structure that includes a semiconductor material layer 322 and a conductive oxide material layer 324. In embodiments, semiconductor material layer 322 includes one or more of amorphous silicon, amorphous tantalum nitride, amorphous tantalum silicon nitride, or other similar semiconductor material, and conductive oxide material layer 324 includes one or more of crystalline titanium oxide, crystalline zinc oxide, crystalline tungsten oxide, crystalline praseodymium calcium manganese oxide, or other similar conductive oxide material. Other semiconductor materials and/or conductive oxide materials may be used. As described above, a BMC memory cell includes a barrier modulated switching structure.
Vertical bit lines LBL11-LBL33 are disposed adjacent reversible resistance-switching memory material 214, are formed of a conductive material (e.g., titanium nitride). In an embodiment, each of vertical bit lines LBL11-LBL33 includes an adhesion material layer (not shown) disposed adjacent reversible resistance-switching memory material 214. Vertical bit lines LBL11-LBL33 are separated from one another by a fourth dielectric material layer 326 (e.g., silicon dioxide). In some embodiments, each of a vertical bit lines LBL11-LBL33 includes a vertical structure (e.g., a rectangular prism, a cylinder, or a pillar), and the vertical strip of reversible resistance-switching memory material 214 may completely or partially surround the vertical structure (e.g., a conformal layer of reversible resistance-switching material surrounding the sides of the vertical structure).
A memory cell is disposed between the intersection of each vertical bit line and each word line. For example, a memory cell M111 is disposed between vertical bit line LBL11 and word line WL10, a memory cell M116 is disposed between vertical bit line LBL13 and word line WL13, a memory cell M511 is disposed between vertical bit line LBL11 and word line WL50, a memory cell M536 is disposed between vertical bit line LBL33 and word line WL50, and so on. In an embodiment, monolithic three-dimensional memory array 300 includes ninety memory cells M111, M112, . . . , M536. Persons of ordinary skill in the art will understand that monolithic three-dimensional memory arrays may include more or fewer than ninety memory cells.
In an example, portions of the vertical strip of reversible resistance-switching material 214 may include a part of memory cell M111 associated with the cross section between word line WL10 and LBL11, and a part of memory cell M211 associated with the cross section between word line WL20 and LBL11, and so on.
Each of memory cells M111, M112, . . . , M536 may include a floating gate device, a charge trap device (e.g., using a silicon nitride material), a resistive change memory device, or other type of memory device. Vertically-oriented bit line select transistors Q11-Q33 may be used to select a corresponding one of vertical bit lines LBL11-LBL33. Vertically-oriented bit line select transistors Q11-Q33 may be field effect transistors, although other transistors types may be used.
Thus, the first gate terminal and the second gate terminal of each of vertically-oriented bit line select transistors Q11-Q33 may be used to turn ON and OFF vertically-oriented bit line select transistors Q11-Q3. Without wanting to be bound by any particular theory, for each of vertically-oriented bit line select transistors Q11-Q33, it is believed that the current drive capability of the transistor may be increased by using both the first gate terminal and the second gate terminal to turn ON the transistor. For simplicity, the first and second gate terminal of each of select transistors Q11-Q33 will be referred to as a single gate terminal.
Vertically-oriented bit line select transistors Q11, Q12, Q13 are used to selectively connect/disconnect vertical bit lines LBL11, LBL12, and LBL13 to/from global bit line GBL1 using row select lines SG1, SG2, SG3, respectively. In particular, each of vertically-oriented bit line select transistors Q11, Q12, Q13 has a first terminal (e.g., a drain/source terminal) coupled to a corresponding one of vertical bit lines LBL11, LBL12, and LBL13, respectively, a second terminal (e.g., a source/drain terminal) coupled to global bit line GBL1, and a control terminal (e.g., a gate terminal) coupled to row select line SG1, SG2, SG3, respectively.
Row select lines SG1, SG2, SG3 are used to turn ON/OFF vertically-oriented bit line select transistors Q11, Q12, Q13, respectively, to connect/disconnect vertical bit lines LBL11, LBL12, and LBL13, respectively, to/from global bit line GBL1.
Likewise, vertically-oriented bit line select transistors Q11, Q21, . . . , Q33 are used to selectively connect/disconnect vertical bit lines LBL11, LBL21, and LBL31, respectively, to global bit lines GBL1, GBL2, GBL3, respectively, using row select line SG1. In particular, each of vertically-oriented bit line select transistors Q11, Q21, Q31 has a first terminal (e.g., a drain/source terminal) coupled to a corresponding one of vertical bit lines LBL11, LBL21, and LBL31, respectively, a second terminal (e.g., a source/drain terminal) coupled to a corresponding one of global bit lines GBL1, GBL2, GBL3, respectively, and a control terminal (e.g., a gate terminal) coupled to row select line SG1. Row select line SG1 is used to turn ON/OFF vertically-oriented bit line select transistors Q11, Q21, Q31 to connect/disconnect vertical bit lines LBL11, LBL21, and LBL31, respectively, to/from global bit lines GBL1, GBL2, GBL3, respectively.
Similarly, vertically-oriented bit line select transistors Q13, Q23, Q33 are used to selectively connect/disconnect vertical bit lines LBL13, LBL23, and LBL33, respectively to/from global bit lines GBL1, GBL2, GBL3, respectively, using row select line SG3. In particular, each of vertically-oriented bit line select transistors Q13, Q23, Q33 has a first terminal (e.g., a drain/source terminal) coupled to a corresponding one of vertical bit lines LBL13, LBL23, and LBL33, respectively, a second terminal (e.g., a source/drain terminal) coupled to a corresponding one of global bit lines GBL1, GBL2, GBL3, respectively, and a control terminal (e.g., a gate terminal) coupled to row select line SG3. Row select line SG3 is used to turn ON/OFF vertically-oriented bit line select transistors Q13, Q23, Q33 to connect/disconnect vertical bit lines LBL13, LBL23, and LBL33, respectively, to/from global bit lines GBL1, GBL2, GBL3, respectively.
One previously known monolithic three-dimensional memory array, such as monolithic three-dimensional array 202 of FIG. 2B, includes titanium nitride word lines and titanium nitride bit lines. BMC memory cells formed using BMC memory elements disposed between titanium nitride word lines and titanium nitride bit lines have been shown to require high operation bias voltages for SET and RESET operations (e.g., SET >5V and RESET >6V). For many applications, such high operating bias voltages are too prohibitive.
Technology is described for forming BMC memory cells that include word lines made from a first conductive material having a first work function, and bit lines made from a second conductive material having a second work function, with the first work function greater than the second work function. In an embodiment, the first work function is greater than the second work function by at least about 200 mV.
In an embodiment, technology is described for forming BMC memory cells that include tungsten or tungsten nitride word lines and titanium nitride bit lines. Alternatively, word lines may be fabricated from cobalt, ruthenium, or other similar material, and bit lines may be fabricated from tantalum nitride, tantalum carbide, titanium carbide, or other similar material. Without wanting to be bound by any particular theory, it is believed that by using word lines fabricated from a conductive material having a higher work function than that of the bit lines, reduced operating bias voltages may be used for SET and RESET operations.
In particular, referring now to FIGS. 4A1-4J2, an example method of forming a monolithic three-dimensional memory array, such as monolithic three-dimensional array 300 of FIGS. 3A-3E, is described.
With reference to FIGS. 4A1-4A3, substrate 302 is shown as having already undergone several processing steps. Substrate 302 may be any suitable substrate such as a silicon, germanium, silicon-germanium, undoped, doped, bulk, silicon-on-insulator (“SOI”) or other substrate with or without additional circuitry. For example, substrate 302 may include one or more n-well or p-well regions (not shown). Isolation layer 304 is formed above substrate 302. In some embodiments, isolation layer 304 may be a layer of silicon dioxide, silicon nitride, silicon oxynitride or any other suitable insulating layer.
Following formation of isolation layer 304, a conductive material layer 306 is deposited over isolation layer 304. Conductive material layer 306 may include any suitable conductive material such as tungsten or another appropriate metal, heavily doped semiconductor material, a conductive silicide, a conductive silicide-germanide, a conductive germanide, or the like deposited by any suitable method (e.g., CVD, PVD, etc.). In at least one embodiment, conductive material layer 306 may comprise between about 200 and about 2500 angstroms of tungsten. Other conductive material layers and/or thicknesses may be used. In some embodiments, an adhesion layer (not shown), such as titanium nitride or other similar adhesion layer material, may be disposed between isolation layer 304 and conductive material layer 306, and/or between conductive material layer 306 and subsequent vertically-oriented bit line select transistors layers.
Persons of ordinary skill in the art will understand that adhesion layers may be formed by PVD or another method on conductive material layers. For example, adhesion layers may be between about 20 and about 500 angstroms, and in some embodiments about 100 angstroms, of titanium nitride or another suitable adhesion layer such as tantalum nitride, tungsten nitride, tungsten, molybdenum, combinations of one or more adhesion layers, or the like. Other adhesion layer materials and/or thicknesses may be employed.
Following formation of conductive material layer 306, conductive material layer 306 is patterned and etched. For example, conductive material layer 306 may be patterned and etched using conventional lithography techniques, with a soft or hard mask, and wet or dry etch processing. In at least one embodiment, conductive material layer 306 is patterned and etched to form global bit lines GBL1, GBL2, GBL3. Example widths for global bit lines GBL1, GBL2, GBL3 and/or spacings between global bit lines GBL1, GBL2, GBL3 range between about 200 angstroms and about 1000 angstroms, although other conductor widths and/or spacings may be used.
After global bit lines GBL1, GBL2, GBL3 have been formed, a first dielectric material layer 308 is formed over substrate 302 to fill the voids between global bit lines GBL1, GBL2, GBL3. For example, approximately 3000-7000 angstroms of silicon dioxide may be deposited on the substrate 302 and planarized using chemical mechanical polishing or an etchback process to form a planar surface 400. Other dielectric materials such as silicon nitride, silicon oxynitride, low K dielectrics, etc., and/or other dielectric material layer thicknesses may be used. Example low K dielectrics include carbon doped oxides, silicon carbon layers, or the like.
In other embodiments, global bit lines GBL1, GBL2, GBL3 may be formed using a damascene process in which first dielectric material layer 308 is formed, patterned and etched to create openings or voids for global bit lines GBL1, GBL2, GBL3. The openings or voids then may be filled with conductive layer 306 (and/or a conductive seed, conductive fill and/or barrier layer if needed). Conductive material layer 306 then may be planarized to form planar surface 400.
Following planarization, the semiconductor material used to form vertically-oriented bit line select transistors Q11-Q33 is formed over planar surface 400 of substrate 302. In some embodiments, each vertically-oriented bit line select transistor is formed from a polycrystalline semiconductor material such as polysilicon, an epitaxial growth silicon, a polycrystalline silicon-germanium alloy, polygermanium or any other suitable material. Alternatively, vertically-oriented bit line select transistors Q11-Q33 may be formed from a wide band-gap semiconductor material, such as ZnO, InGaZnO, or SiC, which may provide a high breakdown voltage, and typically may be used to provide junctionless FETs. Persons of ordinary skill in the art will understand that other materials may be used.
In some embodiments, each vertically-oriented bit line select transistor Q11-Q33 may include a first region (e.g., p+ polysilicon), a second region (e.g., intrinsic polysilicon) and a third region (e.g., p+ polysilicon) to form drain/source, body, and source/drain regions, respectively, of a vertical FET. For example, a heavily doped p+ polysilicon layer 402 may be deposited on planar surface 400. P+ silicon may be either deposited and doped by ion implantation or may be doped in situ during deposition to form p+ polysilicon layer 402.
For example, an intrinsic silicon layer may be deposited on planar surface 400, and a blanket p-type implant may be employed to implant boron a predetermined depth within the intrinsic silicon layer. Example implantable molecular ions include BF2, BF3, B and the like. In some embodiments, an implant dose of about 1-10×1013 ions/cm2 may be employed. Other implant species and/or doses may be used. Further, in some embodiments, a diffusion process may be employed. In an embodiment, the resultant p+ polysilicon layer 402 has a thickness of from about 50 angstroms to about 300 angstroms, although other layer thicknessess may be used.
Following formation of p+ polysilicon layer 402, an intrinsic (undoped) or lightly doped polysilicon layer 404 is deposited on p+ polysilicon layer 402. In some embodiments, intrinsic layer 404 is in an amorphous state as deposited. In other embodiments, intrinsic layer 404 is in a polycrystalline state as deposited. CVD or another suitable process may be employed to deposit intrinsic layer 404. In an embodiment, intrinsic layer 404 has a thickness between about 1000 angstroms to about 3000 angstroms, although other layer thicknesses may be used.
After deposition of intrinsic layer 404, a p+ polysilicon layer 406 may be formed over intrinsic layer 404. P-type silicon may be either deposited and doped by ion implantation or may be doped in situ during deposition to form a p+ polysilicon layer 406.
For example, an intrinsic silicon layer may be deposited on intrinsic layer 404, and a blanket p-type implant may be employed to implant boron a predetermined depth within the intrinsic silicon layer. Example implantable molecular ions include BF2, BF3, B and the like. In some embodiments, an implant dose of about 1-10×1013 ions/cm2 may be employed. Other implant species and/or doses may be used. Further, in some embodiments, a diffusion process may be employed. In an embodiment, the resultant p+ polysilicon layer 406 has a thickness of from about 50 angstroms to about 300 angstroms, although other p-type silicon layer sizes may be used.
Following formation of p+ polysilicon layer 406, silicon layers 402, 404 and 406 are patterned and etched to form vertical transistor pillars. For example, silicon layers 402, 404 and 406 may be patterned and etched using conventional lithography techniques, with wet or dry etch processing. In an embodiment, silicon layers 402, 404 and 406 are patterned and etched to form vertical transistor pillars disposed above global bit lines GBL1, GBL2, GBL3. The vertical transistor pillars will be used to form vertically-oriented bit line select transistors Q11-Q33.
Silicon layers 402, 404 and 406 may be patterned and etched in a single pattern/etch procedure or using separate pattern/etch steps. Any suitable masking and etching process may be used to form vertical transistor pillars. For example, silicon layers may be patterned with about 0.1 to about 1.5 micron of photoresist (“PR”) using standard photolithographic techniques. Thinner PR layers may be used with smaller critical dimensions and technology nodes. In some embodiments, an oxide hard mask may be used below the PR layer to improve pattern transfer and protect underlying layers during etching.
In some embodiments, after etching, the vertical transistor pillars may be cleaned using a dilute hydrofluoric/sulfuric acid clean. Such cleaning may be performed in any suitable cleaning tool, such as a Raider tool, available from Semitool of Kalispell, Mont. Example post-etch cleaning may include using ultra-dilute sulfuric acid (e.g., about 1.5 1.8 wt %) for about 60 seconds and/or ultra-dilute hydrofluoric (“HF”) acid (e.g., about 0.4-0.6 wt %) for 60 seconds. Megasonics may or may not be used. Other clean chemistries, times and/or techniques may be employed.
A gate dielectric material layer 314 is deposited conformally over substrate 302, and forms on sidewalls of the vertical transistor pillars. For example, between about 30 angstroms to about 100 angstroms of silicon dioxide may be deposited. Other dielectric materials such as silicon nitride, silicon oxynitride, low K dielectrics, etc., and/or other dielectric material layer thicknesses may be used.
Gate electrode material is deposited over the vertical transistor pillars and gate dielectric material layer 314 to fill the voids between the vertical transistor pillar. For example, approximately 10 nm to about 20 nm of titanium nitride or other similar metal, a highly-doped semiconductor, such as n+ polysilicon, p+ polysilicon, or other similar conductive material may be deposited. The as-deposited gate electrode material is subsequently etched back to form row select lines SG1, SG2, SG3.
A second dielectric material layer 310 is deposited over substrate 302. For example, approximately 5000 to about 8000 angstroms of silicon dioxide may be deposited and planarized using chemical mechanical polishing or an etch-back process to form planar top surface 408, resulting in the structure shown in FIGS. 4A1-4A3. Other dielectric materials and/or thicknesses may be used.
Planar surface 408 includes exposed top surfaces of vertically-oriented bit line select transistors Q11-Q33 and gate dielectric material layer 314 separated by second dielectric material layer 310. Other dielectric materials such as silicon nitride, silicon oxynitride, low K dielectrics, etc., and/or other dielectric material layer thicknesses may be used. Example low K dielectrics include carbon doped oxides, silicon carbon layers, or the like.
A first etch stop layer 316 (e.g., aluminum oxide) is formed over planar top surface 408. A stack of alternating layers of third dielectric material layer 318 and a sacrificial material layer 410 are formed over planar top surface 408. Third dielectric material layers 318 may be silicon dioxide or other dielectric material. Sacrificial material layers 410 may include any suitable sacrificial material layers formed by any suitable method (e.g., CVD, PVD, etc.). Sacrificial material layers 410 each may be a nitride material, such as silicon nitride, a silicate glass, such as borophosphosilicate glass, a semiconductor material, such as amorphous silicon or polysilicon, or another semiconductor material, such as a group IV semiconductor, including silicon-germanium and germanium, or other sacrificial material.
In an embodiment, each third dielectric material layer 318 may be between about 50 angstroms and about 250 angstroms of SiO2, and each sacrificial material layer 410 may be between about 50 angstroms and about 300 angstroms of silicon nitride. Other dielectric materials and/or thicknesses and other sacrificial materials and/or thicknesses may be used. In an embodiment, five sacrificial material layers 410 are formed over substrate 302. More or fewer than five sacrificial material layers 410 may be used.
Next, a second etch stop layer 320 is formed over substrate 302, resulting in the structure shown in FIGS. 4B1-4B2. Second etch stop layer 320 may include any suitable etch stop layer formed by any suitable method (e.g., CVD, PVD, etc.). In an embodiment, second etch stop layer 320 may be between about 50 angstroms and about 500 angstroms of polysilicon. Other etch stop layer materials and/or thicknesses may be used.
Next, second etch stop layer 320, third dielectric material layers 318, and sacrificial material layers 410 are patterned and etched to form rows 412, with voids 414 separating rows 412, resulting in the structure shown in FIGS. 4C1-4C3. Each of rows 412 may be between about 200 angstroms and about 1000 angstroms wide, although other widths may be used. Voids 414 may be between about 100 angstroms and about 800 angstroms wide, although other widths may be used.
A fourth dielectric material 326 is deposited over substrate 302, filling voids 414 between rows 412. For example, approximately 3000-7000 angstroms of silicon dioxide may be deposited on the substrate 302 and planarized using chemical mechanical polishing or an etchback process to form a planar surface 416, resulting in the structure shown in FIGS. 4D1-4D3. Other dielectric materials such as silicon nitride, silicon oxynitride, low K dielectrics, etc., and/or other dielectric material layer thicknesses may be used. Example low K dielectrics include carbon doped oxides, silicon carbon layers, or the like.
Next, fourth dielectric material 326 is patterned and etched to first etch stop layer 316 to form holes 418 disposed above vertically-oriented bit line select transistors Q11-Q33, resulting in the structure shown in FIGS. 4E1-4E4. Although holes 418 are shown having a rectangular shape, other shapes may be used. In an embodiment, holes 418 may have a width and a length of between about 200 angstroms and about 1000 angstroms. Other widths may be used.
An etch is used to remove sacrificial material layers 410 via holes 418 to form cavities 420, resulting in the structure shown in FIGS. 4F1-4F4. In an embodiment, a wet etch may be used to remove sacrificial material layers 410. In other embodiments, wet and/or dry etch chemistries may be used to remove sacrificial material layers 410.
Next, a first conductive material layer having a first work function φ1 is deposited over substrate 302 to fill cavities 420 via holes 418. In an embodiment, cavities 420 may be lined with barrier and seeding layers, and first conductive material layers, such as tungsten, tungsten nitride, cobalt, ruthenium, or other similar material are formed on the barrier and seeding layers. The barrier and seeding layers and conductive material layers form word lines WL10, WL11, . . . , WL53, resulting in the structure shown in FIGS. 4G1-4G4.
A nonvolatile memory material layer 214 is deposited conformally over substrate 302. Non-volatile memory material 214 may include, for example, an oxide layer, a reversible resistance-switching material (e.g., one or more metal oxide layers such as nickel oxide, hafnium oxide, or other similar metal oxide materials, a phase change material, a barrier modulated switching structure or other similar reversible resistance-switching memory material), a ferroelectric material, or other nonvolatile memory material.
In an embodiment, each vertical strip of non-volatile memory material 214 includes a barrier modulated switching structure that includes a semiconductor material layer 322 and a conductive oxide material layer 324. In embodiments, semiconductor material layer 322 includes one or more of amorphous silicon, amorphous tantalum nitride, amorphous tantalum silicon nitride, or other similar semiconductor material, and conductive oxide material layer 324 includes one or more of crystalline titanium oxide, crystalline zinc oxide, crystalline tungsten oxide, crystalline praseodymium calcium manganese oxide, or other similar conductive oxide material. Other semiconductor materials and/or conductive oxide materials may be used.
For example, between about 10 angstroms to about 100 angstroms of amorphous silicon may be deposited to form semiconductor material layer 322, and between about 50 angstroms and about 150 angstroms of crystallized titanium oxide may be deposited over semiconductor material layer 322 to form conductive oxide material layer 324. Other semiconductor materials such as amorphous tantalum nitride, amorphous tantalum silicon nitride, or other similar semiconductor material, other conductive oxide materials such as crystalline zinc oxide, crystalline tungsten oxide, crystalline praseodymium calcium manganese oxide, or other similar conductive oxide material and/or other material layer thicknesses may be used.
An anisotropic etch is used to remove lateral portions of semiconductor material layer 322 and conductive oxide material 324, leaving only sidewall portions of semiconductor material layer 322 and conductive oxide material 324, resulting in the structure shown in FIGS. 4H1-4H2.
Next, first etch stop layer 316 is patterned and etched to expose top surfaces of bit line select transistors Q11-Q31, resulting in the structure shown in FIGS. 4I1-4I2.
Next, a second conductive material having a second work function φ2 (e.g., titanium nitride, tantalum nitride, titanium carbide, tantalum carbide, or other conductive material) is deposited over substrate 302, filling holes 422 and forming vertical bit lines LBL11-LBL33. In an embodiment, first work function φ1 of the first conductive material used to form word lines WL10, WL11, . . . , WL53 is greater than second work function φ2 of the second conductive material used to form vertical bit lines LBL11-LBL33. In an embodiment, first work function φ1 is greater than second work φ2 function by at least about 200 mV. The structure is then planarized using chemical mechanical polishing or an etch-back process, resulting in the structure shown in FIGS. 4J1-4J2.
Thus, as described above, one embodiment of the disclosed technology includes a method that includes forming a dielectric material above a substrate, forming a hole in the dielectric material, the hole disposed in a first direction, forming a word line layer above the substrate via the hole, the word line layer disposed in a second direction perpendicular to the first direction, the word line layer including a first conductive material having a first work function, forming a nonvolatile memory material on a sidewall of the hole, the nonvolatile memory material including a semiconductor material layer and a conductive oxide material layer, forming a local bit line in the hole, the local bit line including a second conductive material having a second work function, wherein the first work function is greater than the second work function, and forming a memory cell comprising the nonvolatile memory material at an intersection of the local bit line and the word line layer.
One embodiment of the disclosed technology includes a method including forming a sacrificial material layer above a substrate, etching the sacrificial material layer to form a row of sacrificial material disposed in a first direction, forming a dielectric material adjacent the row of sacrificial material, forming a hole in the dielectric material, the hole adjacent the row of sacrificial material and disposed in a second direction perpendicular to the first direction, replacing the row of sacrificial material with a first conductive material to form a word line layer, the first conductive material including a first work function, forming a nonvolatile memory material on a sidewall of the hole, the nonvolatile memory material including a semiconductor material layer and a conductive oxide material layer, forming a local bit line in the hole, the local bit line including a second conductive material having a second work function, wherein the first work function is greater than the second work function, and forming a memory cell including the nonvolatile memory material at an intersection of the local bit line and the word line layer.
One embodiment of the disclosed technology includes method of forming a monolithic three-dimensional memory array, the method including forming a stack of sacrificial material layers above a substrate; etching the stack of sacrificial material layers to form rows of sacrificial material layers; forming a dielectric material between the rows of sacrificial material layers; forming a plurality of holes in the dielectric material, the holes disposed between the rows of sacrificial material layers; removing the rows of sacrificial material layers via the plurality of holes to form a plurality of cavities; forming a first conductive material in each of the cavities to form a plurality of word line layers, the first conductive material having a first work function; forming a nonvolatile memory material on a sidewall of each of the plurality of holes, the nonvolatile memory material including a semiconductor material layer and a conductive oxide material layer; forming a plurality of local bit lines in the plurality of holes, the local bit lines including a second conductive material having a second work function, wherein the first work function is greater than the second work function, and forming an array of memory cells, each memory cell including the nonvolatile memory material at an intersection of one of the plurality of local bit lines and one of the plurality of word line layers.
For purposes of this document, each process associated with the disclosed technology may be performed continuously and by one or more computing devices. Each step in a process may be performed by the same or different computing devices as those used in other steps, and each step need not necessarily be performed by a single computing device.
For purposes of this document, reference in the specification to “an embodiment,” “one embodiment,” “some embodiments,” or “another embodiment” may be used to described different embodiments and do not necessarily refer to the same embodiment.
For purposes of this document, a connection can be a direct connection or an indirect connection (e.g., via another part).
For purposes of this document, the term “set” of objects may refer to a “set” of one or more of the objects.
Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

## Claims

1. A method comprising:
forming a dielectric material above a substrate;
forming a hole in the dielectric material, the hole disposed in a first direction;
forming a word line layer above the substrate via the hole, the word line layer disposed in a second direction perpendicular to the first direction, the word line layer comprising a first conductive material having a first work function;
forming a nonvolatile memory material on a sidewall of the hole, the nonvolatile memory material comprising a semiconductor material layer and a conductive oxide material layer;
forming a local bit line in the hole, the local bit line comprising a second conductive material having a second work function, wherein the first work function is greater than the second work function; and
forming a memory cell comprising the nonvolatile memory material at an intersection of the local bit line and the word line layer.

2. The method of claim 1, further comprising:
forming a plurality of word line layers above the substrate via the hole, each of the plurality of word line layers disposed in the second direction; and
forming a plurality of memory cells comprising the nonvolatile memory material, each of the memory cells formed at an intersection of the local bit line and a corresponding one of the word line layers.

3. The method of claim 1, further comprising:
forming a plurality of holes in the dielectric material, the plurality of holes disposed in the second direction;
forming the word line layer via the plurality of holes;
forming a nonvolatile memory material on a sidewall of each of the holes;
forming a plurality of local bit lines, each local bit line disposed in a corresponding one of the holes; and
forming a plurality of memory cells comprising the nonvolatile memory material, each of the memory cells formed at an intersection of the word line layer and a corresponding one of the local bit lines.

4. The method of claim 1, further comprising forming a vertically-oriented transistor above the substrate, and wherein forming the hole comprises forming the hole above the vertically-oriented transistor.

5. The method of claim 1, further comprising:
forming a global bit line above the substrate, the global bit line disposed in a third direction perpendicular to the first direction and the second direction; and
forming a transistor between the vertical bit line and the global bit line.

6. The method of claim 5, wherein the transistor comprises a vertical transistor.

7. The method of claim 1, further comprising:
forming a sacrificial material layer above the substrate;
removing the sacrificial material layer to form a cavity; and
forming the word line layer in the cavity.

8. The method of claim 7, wherein removing the sacrificial material layer comprises etching the sacrificial material layer via the hole.

9. The method of claim 1, wherein:
the semiconductor material layer comprises one or more of the group of amorphous silicon, amorphous tantalum nitride, and amorphous tantalum silicon nitride; and
the conductive oxide material layer comprises one or more of the group of crystalline titanium oxide, crystalline zinc oxide, crystalline tungsten oxide, and crystalline praseodymium calcium manganese oxide.

10. The method of claim 1, wherein:
the first conductive material comprises one or more of the group of tungsten, tungsten nitride, cobalt, and ruthenium; and
the second conductive material comprises one or more of the group of titanium nitride, tantalum nitride, titanium carbide, and tantalum carbide.

11. A method comprising:
forming a sacrificial material layer above a substrate;
etching the sacrificial material layer to form a row of sacrificial material disposed in a first direction;
forming a dielectric material adjacent the row of sacrificial material;
forming a hole in the dielectric material, the hole adjacent the row of sacrificial material and disposed in a second direction perpendicular to the first direction;
replacing the row of sacrificial material with a first conductive material to form a word line layer, the first conductive material comprising a first work function;
forming a nonvolatile memory material on a sidewall of the hole, the nonvolatile memory material including a semiconductor material layer and a conductive oxide material layer;
forming a local bit line in the hole, the local bit line including a second conductive material having a second work function, wherein the first work function is greater than the second work function; and
forming a memory cell comprising the nonvolatile memory material at an intersection of the local bit line and the word line layer.

12. The method of claim 11, wherein the sacrificial material comprises one or more of the group of a nitride, a silicate glass and a semiconductor material.

13. The method of claim 11, further comprising:
forming a plurality of sacrificial material layers above the substrate;
etching the plurality of sacrificial material layers to form a row of sacrificial material layers disposed in the first direction;
replacing each of the sacrificial material layers with the first conductive material to form a plurality of word line layers; and
forming a plurality of memory cells comprising the nonvolatile memory material, each of the memory cells formed at an intersection of the local bit line and a corresponding one of the word line layers.

14. The method of claim 11, further comprising:
forming a plurality of holes in the dielectric material, the plurality of holes disposed in the first direction, each of the holes adjacent the row of sacrificial material;
forming a nonvolatile memory material on a sidewall of each of the holes;
forming a plurality of local bit lines, each local bit line disposed in a corresponding one of the holes; and
forming a plurality of memory cells comprising the nonvolatile memory material, each of the memory cells formed at an intersection of the word line layer and a corresponding one of the local bit lines.

15. The method of claim 11, wherein replacing the sacrificial material layer comprises:
removing the sacrificial material layer to form a cavity; and
forming the conductive material in the cavity.

16. The method of claim 15, wherein removing the sacrificial material layer comprises etching the sacrificial material layer via the hole.

17. The method of claim 11, wherein:
the semiconductor material layer comprises one or more of the group of amorphous silicon, amorphous tantalum nitride, and amorphous tantalum silicon nitride; and
the conductive oxide material layer comprises one or more of the group of crystalline titanium oxide, crystalline zinc oxide, crystalline tungsten oxide, and crystalline praseodymium calcium manganese oxide.

18. The method of claim 11, wherein:
the first conductive material comprises one or more of the group of tungsten, tungsten nitride, cobalt, and ruthenium; and
the second conductive material comprises one or more of the group of titanium nitride, tantalum nitride, titanium carbide, and tantalum carbide.

19. A method of forming a monolithic three-dimensional memory array, the method comprising:
forming a stack of sacrificial material layers above a substrate;
etching the stack of sacrificial material layers to form rows of sacrificial material layers;
forming a dielectric material between the rows of sacrificial material layers;
forming a plurality of holes in the dielectric material, the holes disposed between the rows of sacrificial material layers;
removing the rows of sacrificial material layers via the plurality of holes to form a plurality of cavities;
forming a first conductive material in each of the cavities to form a plurality of word line layers, the first conductive material having a first work function;
forming a nonvolatile memory material on a sidewall of each of the plurality of holes, the nonvolatile memory material including a semiconductor material layer and a conductive oxide material layer;
forming a plurality of local bit lines in the plurality of holes, the local bit lines including a second conductive material having a second work function, wherein the first work function is greater than the second work function; and
forming an array of memory cells, each memory cell comprising the nonvolatile memory material at an intersection of one of the plurality of local bit lines and one of the plurality of word line layers.

20. The method of claim 19, wherein:
the semiconductor material layer comprises one or more of the group of amorphous silicon, amorphous tantalum nitride, and amorphous tantalum silicon nitride; and
the conductive oxide material layer comprises one or more of the group of crystalline titanium oxide, crystalline zinc oxide, crystalline tungsten oxide, and crystalline praseodymium calcium manganese oxide.